Catheter with physiological sensor

ABSTRACT

The disclosed embodiments present improved catheters with physiological sensors. In one embodiment, the catheter includes, generally, a pressure transducer/electronics assembly connected to a pressure transmission catheter. The pressure transmission catheter includes a hollow tube made from a low compliance material. The distal end of the hollow tube is filled with a gel-like material or plug which acts as a barrier between the catheter liquid and the target fluid. The hollow tube is partially filled with a low viscosity liquid and is in fluid communication with the gel-like material and the pressure transducer. The pressure of the target fluid is transmitted to the liquid in the hollow tube through the gel-like material and/or the wall of the distal tip and is fluidically transmitted to the pressure transducer. The pressure transmission catheter may be inserted into a vessel lumen or into a lumen of a therapeutic or diagnostic catheter for biomedical applications.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present invention is a continuation of U.S. patent application Ser.No. 09/825,130, filed on Apr. 3, 2001, now U.S. Pat. No. 6,659,959,which is a continuation of U.S. patent application Ser. No. 09/264,147,filed on Mar. 5, 1999, now issued as U.S. Pat. No. 6,296,615, thespecifications of which are incorporated herein by reference.

The present invention is also related to U.S. patent application Ser.No. 09/159,653, filed on Sep. 24, 1998, now issued as U.S. Pat. No.6,409,674, the specification of which is incorporated herein byreference.

TECHNICAL FIELD

The described embodiments generally relate to catheters, and moreparticularly, to catheters capable of sensing physiological pressures,such as blood pressure, intracranial pressure, intrapleural pressure,bladder pressure, and pressure within the gastro-intestinal system, andof sensing an electric signal, such as an electrocardiogram.

BACKGROUND

U.S. Pat. No. 4,846,191, of Brian P. Brockway et al. (hereinafter theBrockway et al. '191 patent) discloses a pressure measurement device forsensing physiological pressures. The device consists generally of apressure transducer with associated electronics and a pressuretransmission catheter. The distal tip of the catheter senses thepressure of the target site and transmits the pressure fluidicallythrough the catheter to be sensed by the pressure transducer.

In one embodiment of the Brockway et al. '191 patent, the pressuretransmission catheter consists of a small diameter hollow tube which isfilled with a low viscosity liquid. This liquid is in fluidcommunication with the pressure transducer at the proximal end of thehollow tube and a gel-like material at the distal end. The gel-likematerial provides a direct interface with the tissue or body fluid ofwhich the pressure is to be measured.

Pressure measurement catheters such as described in the Brockway et al.'191 patent have been used to augment/support therapeutic treatments, aswell as provide valuable information for diagnosis. For example, bloodpressure measurements are very important when percutaneous therapeuticcatheters affect blood pressure. Examples of therapeutic cathetersinclude intra-aortic balloon catheters, angioplasty catheters, andperfusion catheters.

Taking one type of therapeutic catheter as an example, intra-aorticballoon catheters are designed to assist a failing heart through cyclicinflation/deflation of a balloon placed in the descending thoracicaorta, in counterpulsation to the heart. In a typical procedure, aguidewire (a thin flexible wire) is inserted through an incision intothe common femoral artery and is directed through the delicate, tortuousand narrow vasculature. Once the guidewire is positioned, theintra-aortic balloon catheter is passed over the guidewire, utilizingthe guidewire lumen of the catheter, until the balloon reaches thedesired location.

The balloon is connected through a series of thin tubes to a controlsystem which controls the balloon's inflation and deflation, repeatedly,in synchrony with a patient's heart beat. The action of the balloonassumes some of the load of the heart mainly by increasing systolicpressure which increases the flow of blood through the coronaryarteries. In order to synchronize the balloon inflation/deflation withthe heart beat, the patient's heart electric signal or electrocardiogramis detected using surface electrodes attached to the skin of thepatient. These electrodes are connected to the control system of theintra-aortic balloon catheter. Inflation of the balloon occurs at aspecified time relative to a reference signal on the patient'selectrocardiogram.

The intra-aortic balloon catheter system of the Brockway et al. '191patent, as described above, has its limitations. For example, thesurface electrodes used to detect the patient's electrocardiogram forballoon inflation/deflation control have a limitation in that the signalcan be relatively weak and noisy, leading potentially to spurious orunreliable responses. Further, the electrodes may become disengaged fromthe patient's skin due to lack of adhesion or being knocked off.Additionally, the patient typically has one set of surface electrodesattached for general monitoring; adding a second set of electrodes forcontrolling the intra-aortic balloon catheter adds further complexityand discomfort for the patient.

Blood pressure is typically used to calibrate the intra-aortic ballooncatheter system. Ideally, this pressure should be measured in thevicinity of the catheter balloon. The electric signals sensed by theelectrodes are used as the primary trigger for the catheter controlsystem to pneumatically inflate the balloon, and the pressure signalsare used to temporally calibrate balloon inflation to the electricalsignals.

In the treatment modality of the Brockway et al. '191 patent, once thetherapeutic catheter is placed, the guidewire is removed from thecatheter's guidewire lumen. The guidewire lumen is then flushed withsaline, or saline with anticoagulation agents such as heparin, in orderto “fill” the guidewire lumen with a liquid. Once filled, the proximalend of the catheter is connected to a pressure transducer. In thisrespect, blood pressure upstream of the balloon is fluidicallytransmitted through the saline and detected by the pressure transducer.

This approach has its limitations for accurately measuring the pressure,especially with smaller balloon catheters having small guidewire lumens.Limitations may include high system compliance, the presence of airbubbles in the guidewire lumen, and possible blood coagulation in theguidewire lumen. Compliance is a property of this measurement systemthat provides a measure of resistance to deformation due to pressure. Asystem with high compliance will deform more than a low compliancesystem as pressure is increased. A high compliance system will tend toabsorb rapid pressure changes that should be transmitted through theliquid in the lumen. This, in turn, reduces the accuracy of the pressuremeasurements as a result of lowering the frequency response. Excessiveair bubbles and thrombus in the guidewire lumen can also result indampening and loss of accuracy of the measured blood pressure signal.This can reduce the efficacy of the inflation of the balloon.

A further limitation of the system of the Brockway et al. '191 patent isthat it is labor intensive. There is the additional preparation requiredby the user to fill the guidewire lumen just prior to use. Improperfilling may lead to bubble formation in the catheter lumen. It is alsonecessary to flush the lumen to remove thrombus that may form, otherwisethe pressure signal might be blocked altogether.

What is needed is an improved apparatus to obtain more reliable andhigher quality measurements of blood pressure. An improved apparatus forsensing an electric signal is also needed.

SUMMARY

The disclosed embodiments present improved catheters with physiologicalsensors. In one embodiment, the catheter includes, generally, a pressuretransducer/electronics assembly connected to a pressure transmissioncatheter. The pressure transmission catheter includes a hollow tube madefrom a low compliance material. The distal end of the hollow tube isfilled with a gel-like material or plug which acts as a barrier betweenthe catheter liquid and the target fluid. The hollow tube is partiallyfilled with a low viscosity liquid and is in fluid communication withthe gel-like material and the pressure transducer. The pressure of thetarget fluid is transmitted to the liquid in the hollow tube through thegel-like material and/or the wall of the distal tip and is fluidicallytransmitted to the pressure transducer. The pressure transmissioncatheter is capable of being used by itself or it can be inserted into alumen of a therapeutic or diagnostic catheter for biomedicalapplications. This provides the ability to directly measure the pressureeffects of the treatment catheter.

In another embodiment, the distal end of the pressure transmissioncatheter may be electrically conductive so as to detect and transmitelectrical signals. Thus, in this embodiment, the catheter can be usedto detect a physiological parameter manifested as an electrical current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional side view of an embodiment of apressure sensing catheter.

FIG. 2 is a partial cross-sectional side view of an embodiment of apressure sensing catheter.

FIG. 3 is a partial cross-sectional side view of an embodiment of apressure and electric signal sensing catheter.

FIG. 4 is a partial cross-sectional side view of an embodiment of apressure and electric signal sensing catheter.

FIG. 5 is a partial cross-sectional side view of an embodiment of apressure and electric signal sensing catheter.

FIG. 6 is a cross-sectional side view of an embodiment of a distal endof the pressure and electric signal sensing catheter of FIG. 5.

FIG. 7 is a partial cross-sectional side view of an embodiment of adistal end of a catheter with a physiological sensor.

FIG. 8 is a partial cross-sectional side view of an embodiment of adistal end of a catheter with a physiological sensor.

FIG. 9 is a partial cross-sectional side view of an embodiment of adistal end of a catheter with a physiological sensor.

FIG. 10 is a partial cross-sectional side view of an embodiment of adistal end of a catheter with a physiological sensor.

FIG. 11A is a partial cross-sectional side view of an embodiment of adistal end of a catheter with a physiological sensor.

FIG. 11B is a cross-sectional view at line 11B of the distal end of theembodiment of a catheter with a physiological sensor of FIG. 11A.

FIG. 12 is a partial cross-sectional side view of an embodiment of adistal end of a catheter with a physiological sensor.

FIG. 13 is a side view, partly in section, of an embodiment of apressure and electric signal sensing catheter inserted within a lumen ofa therapeutic catheter.

FIG. 14 is a representation showing an embodiment of a pressure andelectric signal sensing catheter threaded through an intra-aorticballoon catheter lumen, the balloon catheter having first been insertedinto the femoral artery and advanced up to the descending aorta.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which are not necessarily to scale, which form apart hereof, and in which is shown by way of illustrating specificembodiments in which the device may be practiced. These embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the device, and it is to be understood that the embodiments maybe combined, or that other embodiments may be utilized and thatstructural and electrical changes may be made without departing from thespirit and scope. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope is defined by theappended claims and their equivalents. In the drawings, like numeralsdescribe substantially similar components throughout the several views.

The present apparatus and methods will be described in applicationsinvolving biomedical applications. However, it is understood that thepresent apparatus and methods may be employed in other environments anduses.

One embodiment presents a pressure sensing catheter that can be insertedinto and through a lumen of therapeutic/diagnostic catheters. FIG. 1 isa partial cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, one embodiment of portions of apressure sensing catheter 110. Pressure sensing catheter 110 comprises,generally, a pressure transducer/electronics assembly 173 and a pressuretransmitting catheter 114.

Pressure transducer/electronics assembly 173 comprises a main housing179 which contains transducer 142, sensor electrical connections 144,temperature compensation electronics 177, connected to cable 175.Transducer 142 comprises a housing 148, a pressure sensor 174, and anopening 146. Sensor 174 comprises, for example, a silicon diaphragmsensor or other appropriate sensor. Opening 146 provides for a gaugereference pressure. Gauge reference pressure (atmospheric pressure) isused for comparison to the measured pressure. Electronics 177 comprisetemperature compensation circuitry which reduces the effect oftemperature variation on pressure measurements. Cable 175 provides inputpower and also carries output signals to an electric control system fora therapeutic catheter or other such system.

Catheter 114 comprises a long, small-diameter hollow tube 120 having adistal end 122, a proximal end 124, and lumen 121 extending between thedistal end 122 and proximal end 124. The proximal end 124 passes throughLuer lock connector 181 and housing 179 to attach to transducer 142 attube adapter 147 with tube connector 128. Luer lock connector 181 isprovided for connection to other apparatus, such as a therapeuticcatheter having a mating Luer lock connector.

Distal end 122 of catheter 114 contains a thin-walled section 126 wherethe tube wall thickness is reduced. Tube 120 contains a first liquid132, a second liquid 134, and a gel-like material 130. First liquid 132is contained within proximal end 124 and is in fluid contact withpressure sensor 174 substantially filling transducer space 125. Gel-likematerial 130 is contained within distal end 122, but due to pressure andtemperature fluctuations, may move slightly within distal end 122.Second liquid 134 fills the remaining space within hollow tube 120 andis in fluid communication with gel-like material 130 and first liquid132. Thin-wall section 126 also provides the benefit of allowing anincreased surface area of gel-like material 130 exposed to the bodyfluid while allowing the use of a thicker wall in all or some of themain portion of tube 120 in order to minimize compliance. This isespecially relevant when the main portion of hollow tube 120 isconstructed of a relatively compliant material such as a polymer.Thin-wall section 126 also provides a larger cross section of lumen 121compared with proximal end 124. This reduces the movement of gel-likematerial 130 at distal end 122 caused by volumetric changes of firstliquid 132 and second liquid 134.

First liquid 132 and second liquid 134 are low-viscosity,low-vapor-pressure liquids having a minimal compliance and are of acomposition such that they are not soluble in each other. First liquid132 is preferably non-corrosive, hydrophobic, and non-ionic since it maybe in contact with the inner components of transducer 142. Further,first liquid 132 may be chosen to minimize leakage between sensor 174and mount substrate 149.

In some embodiments, first liquid 132 will have the characteristic ofbeing non-electrically conductive (i.e., non-polar and having highdielectric strength). A low-vapor-pressure liquid is desired to keep theamount of trapped air in the sensor to a minimum and to accommodatefilling under vacuum. The low-vapor-pressure liquid is back-filled intotransducer 142, after liquid space 125 has been evacuated. A low vaporpressure allows a higher vacuum to be applied to pressure transducer142, thereby lowering the amount of trapped air. If a fluorinatedhydrocarbon liquid is used as first liquid 132, most or all of theremaining air will be absorbed into the liquid, since it will absorbmore air than most other liquids. This will result in removing most ofthe air bubbles. Lowering the amount of trapped air bubbles reduces thecompliance of the system and as a result improves frequency response. Insome embodiments, first liquid 132 is non-polar, not soluble in secondliquid 134, and hydrophobic, therefore protecting the pressuretransducer die from a potentially polar second liquid 134, bothelectrically and physically.

Second liquid 134 may or may not be electrically conductive. Secondliquid 134 preferably has a low thermal coefficient of expansion, lowviscosity, and low density. The low thermal coefficient of expansionproperty helps to reduce expansion/contraction due to temperaturefluctuations, and therefore reduces the movement of gel-like material130 at distal end 122. Reduction of movement of gel-like material 130 isimportant in order to avoid the formation of a void in gel-like material130 at distal end 122 which may promote the formation of thrombus duringuse and therefore result in loss of performance. Second liquid 134should also be insoluble to gel-like material 130. Low viscosity and lowdensity liquids enable catheter 114 to have a higher frequency response(i.e., bandwidth) due to the reduction of friction and momentum losses.The low density liquid also helps to minimize artifacts due to headpressure.

First liquid 132 and second liquid 134 may comprise, for example, water,saline, inert fluorinated hydrocarbon, silicon oils, alcohols, and watersolutions such as propylene glycol dispersed in water. Both liquids 132and 134 must be non-toxic (in case of leakage). First liquid 132 mayhave a higher coefficient of thermal expansion than second liquid 134.In addition, first liquid 132 should have a low vapor pressure, lowviscosity, and be non-corrosive. Since tube 120 contains substantiallymore second liquid 134, the two-liquid system overall will have a lowercoefficient of expansion and a higher frequency response. This alsogreatly reduces the amount of movement of the gel-like material 130 dueto thermal expansion/contraction of the liquids, resulting in improvedpatency. The use of two liquids also allows the use of a longer andsmaller diameter tube 120 while maintaining a high frequency responseand minimizing movement of gel-like material 130.

Gel-like material 130 is a relatively viscous and hydrophobicliquid/solid material. In one embodiment, gel-like material 130 iscross-linked and has a surface energy which increases its tendency toadhere to the inside walls of distal end 122. Any non-toxic andminimally thrombogenic material capable of flowing as does a viscousliquid and exhibiting intramolecular forces which makes it less likelyto migrate or be dislodged from distal end 122 is acceptable.Additionally, the gel-like material 130 may contain an anti-thrombogenicsubstance to prevent clot formation, such as, for example, heparin andwarfarin.

In some embodiments, tube 120 can be made from any biocompatiblematerial. Tube 120 may have an outside diameter of 0.5 mm and an insidediameter of 0.2 mm. The length of tube 120 depends on the particular useinvolved, but can range from about 5 mm to 4 meters. Tube 120 can bemade from any number of materials that provide the generalcharacteristics of pushability, flexibility, low compliance,biocompatibility, abrasion resistance, ability to contain first liquid132 and second liquid 134, and in some embodiments, be electricallyconductive. Relative stiffness of tube 120 will depend on theapplication. Tube 120 may be very stiff for use where a stiff probe isrequired, or relatively flexible when used, for example, within narrowvasculature or within the lumen of a therapeutic/diagnostic catheter.Materials for tube 120 may include 316 stainless steel, Nitinol,titanium, MP52, MP35N, polyamide, polyimide, impregnated plastic,polytetra fluoroethylene, polyethylene, polyurethane, polyvinylchloride, or polypropylene.

Tube 120, when made from most metals, will have a very low compliancecompared with a tube made from polymer materials. The use of metals, inturn, increases the frequency response of catheter 114. A metal tube 120will also withstand higher torsional and longitudinal stress/strain. Theuse of metal further provides the benefit of a longer and smallerdiameter tube 120 while maintaining good frequency response, due to thelow compliance of the material.

In another embodiment, an antithrombotic coating is applied to pressuretransmission catheter 120. This antithrombotic coating may contain, forexample, heparin, and be attached to tube 120 using, for example, thePhotolink® process (Surmodics, Eden Prairie, Minn.). This will increasethe hemocompatibility of the system. Similarly, a lubricious coating(for example, Parylene C® by Union Carbide) may be applied to catheter120 to reduce friction when sliding catheter 120 into the lumen of atherapeutic/diagnostic catheter. In another embodiment, distal end 122may further comprise a noble metal (such as platinum-iridium) sleeve,ring, or coating. Such a material is known to be antithrombogenic andalso radio-opaque. Radio-opacity may be a benefit while placing thecatheter.

A removable cover 141 is provided to protect distal end 122 whenpackaged and prior to use. Gel-like material 130 is typically rathertacky and would get dirty if not protected. Cover 141 is removed justprior to catheter use. In one embodiment, removable cover 141 iscomprised of silicone tubing that is removed by grasping and pulling offdistal end 122. In another embodiment, cover 141 is comprised of apeel-away cover that can be separated into pieces longitudinally tofacilitate removal.

FIG. 2 shows a side view in partial cross-section illustratinggenerally, by way of example, but not by way of limitation, oneembodiment of portions of a pressure sensing catheter 210. Thisembodiment is similar to the embodiment shown in FIG. 1. Forconvenience, similar components are not described here. In thisembodiment, hollow tube 220 comprises a metal material. Therefore, tube220 contains liquid 234 which is in fluid contact with pressure sensor274 and gel-like material 230.

Liquid 234 has a low thermal coefficient of expansion, low viscosity,low density, and minimal compliance. Liquid 234 is preferablynon-corrosive, and non-ionic since it may be in contact with metalliccomponents of transducer 242. Further, liquid 234 may be chosen tominimize leakage through the joint between transducer 242 and mountsubstrate 249. Liquid 234 may comprise, for example, water, saline,inert fluorinated hydrocarbon, silicon oils, alcohols, and watersolutions such as propylene glycol dispersed in water. Liquid 234 shouldbe non-toxic (in case of leakage) and also be insoluble to gel-likematerial 230.

FIG. 3 shows a side view in partial cross-section illustratinggenerally, by way of example, but not by way of limitation, oneembodiment of portions of a pressure and electrical signal sensingcatheter 310. This embodiment is similar to the embodiment shown inFIG. 1. For convenience, similar components are not described here.

In this embodiment, hollow tube 320 comprises an electrically conductivematerial. Further, catheter 310 includes electrical connections 378coupled to proximal end 324 of hollow tube 320. Hollow tube 320 is alsocoated with electrical insulation layer 338. Since hollow tube 320 iselectrically conductive, it may be used as an electrode to sense andtransmit an electric signal. It may be desired to restrict theelectrical signal sensing portion of electrode 336 to distal end 322.Electric insulation layer 338 covers substantially the entire length oftube 320 except for a portion of tube 320 at distal end 322 or otherportion of interest. This portion is identified as electrode 336.Electrode 336 senses an electrical signal which is electricallytransmitted along tube 320 to electric insulation layer 378. Layer 338may be a coating, a film, or a tube-like component and may be comprisedof, for example, Parylene, silicon nitride, silicon oxide, or Teflon.

External connection 383 is provided as an attachment site for externaldevices, such as, for example, an indifferent electrode. Externalconnection 383 is connected to temperature compensation electronics 377through electrical connection 344. Electrical signals are then able tobe communicated to outside devices though cable 375.

FIG. 4 shows a side view in partial cross-section illustratinggenerally, by way of example, but not by way of limitation, oneembodiment of portions of a pressure and electrical signal sensingcatheter 410. This embodiment is similar to the embodiment shown in FIG.3. For convenience, similar components are not described here. In thisembodiment, hollow tube 420 comprises a metal material. Therefore, tube420 contains liquid 434 which is in fluid contact with pressure sensor474 and gel-like material 430.

Liquid 434 will have the characteristic of being non-electricallyconductive (i.e., non-polar and having high dielectric strength).Additionally, liquid 434 should have a low thermal coefficient ofexpansion, low viscosity, low density, and minimal compliance. Liquid434 is preferably non-corrosive, hydrophobic, and non-ionic since it maybe in contact with metallic components of transducer 442. Further,liquid 434 may be chosen to minimize leakage through the joint betweentransducer 442 and mount substrate 449. Liquid 434 may comprise, forexample, water, saline, inert fluorinated hydrocarbon, silicon oils,alcohols, and water solutions such as propylene glycol dispersed inwater. Liquid 434 should be non-toxic (in case of leakage), and alsoinsoluble to gel-like material 430.

FIG. 5 shows a side view in partial cross-section illustratinggenerally, by way of example, but not by way of limitation, oneembodiment of portions of a pressure and electrical sensing catheter510. Catheter with physiological sensor 510 is comprised generally of apressure transducer/electronics assembly 573 and pressure and electricsignal transmission catheter 514. Assembly 573 comprises pressuretransducer 542, electronics 577, including temperature compensationcircuitry which compensates for variations in ambient temperature, andappropriate electrical connections 544, all housed in main housing 579.Assembly 573 terminates with electrical cable 575 which provides inputpower and also carries output signals to an electric control system fora therapeutic catheter or other such systems. Catheter 514 comprises asmall diameter hollow tube 520 having a distal end 522 and a proximalend 524. The proximal end 524 enters assembly 573 through Luer lock 581.Hollow tube 520 is comprised of an electrically non-conductive material,such as, for example, polyethylene. The electrical characteristics ofthis embodiment are accomplished by embedding a conductor within hollowtube 520, such as shown in FIG. 6, for example.

FIG. 6 shows a side view in partial cross-section illustratinggenerally, by way of example, but not by way of limitation, oneembodiment of the distal portion of the catheter with physiologicalsensor 510 (as shown in FIG. 5). In this embodiment, hollow tube 520comprises an electrically non-conductive material, and further includesan electrically conductive distal end 522, filar coil 645, electricalconnection 639, and tube joint 637. Coil 645 is embedded in tube 520 andruns substantially the entire length of tube 520. At distal end 522,coil 645 terminates at connection 639 and is in electrical communicationwith electrode 635. At proximal end 524 (as shown in FIG. 5), coil 645connects with sensor electrical connection 543. Electrode 635 is aseparate electrically conductive tube that is attached to distal end 522by a joint 637. The electrode 635 senses an electrical signal which iselectrically transmitted along filar coil 645 to connection 543 (asshown in FIG. 5). In other embodiments, electrode 635 may be an integralpart of tube 520, such as, for example, by dispersion of an electricallyconductive material molded into tube 520, and by a deposited layer ofelectrically conductive material. In other embodiments, coil 645 may,for example, be a slender wire that is embedded in, lying outside, orlying inside tube 520. Other methods to electrically communicate anelectric signal from electrode 635 to connection 543, may, for example,include depositing an electrically conductive material as a strip to theoutside of tube 520 and as a dispersion of electrically conductivematerial molded along length of tube 520.

The catheter with physiological sensor may be made from certainmaterials or used in certain circumstances that require the distal endof the catheter to be made more rugged than that provided by anunmodified hollow tube distal portion, with or without a thin-wallsection. A ruggedized feature may be required to resist distal endkinking or collapse. FIG. 7 illustrates generally, by way of example,but not by way of limitation, one embodiment of distal end 722 of acatheter showing ruggedizing feature 790. Distal end 722 can be usedwith the various catheter embodiments shown and described herein.Ruggedizing feature 790 can be attached to distal end 722, over which acompliant membrane 789 is placed. In another embodiment, ruggedizingfeature 790 may be slid over thin wall section 726 to add support todistal end 722, in which case compliant membrane 789 is not needed. Inanother embodiment, ruggedizing feature 790 is created directly fromhollow tube 720 by laser cutting, photo etching, other etching process,molding, or by machining, leaving a mesh-like pattern. Compliantmembrane 789 is then placed on the ruggedized feature, for example, bysputtering, vapor deposition over a mandrel temporally placed in thelumen, dipping, casting over molding, or by sliding over a complianttube, such as heat shrink tubing. In another embodiment, the fabricationprocess does not cut completely through thin wall section 726 but leavesthin compliant areas surrounded by areas of thicker, more rigidmaterial.

Ruggedizing feature 790 comprises a support structure made from arelatively rigid material as compared with thin wall section 726.Ruggedizing feature 790 provides a distal tip 722 that is more resistantto kinking and collapse, while allowing the compliant portion spanningthe spaces within ruggedized feature 790 of thin wall section 726 torespond to pressure, transmitting the pressure to second liquid 734 andto gel-like material 730.

In another embodiment, tube 720 is fabricated of a polymer, such as, forexample, a 60 D hardness urethane that is very flexible. In thisembodiment, ruggedizing feature 790 may be fabricated from a much harderpolymer or from metal.

FIG. 8 illustrates generally, by way of example, but not by way oflimitation, one embodiment of distal end 822 of a catheter showingruggedizing feature 892. Distal end 822 can be used with the variouscatheter embodiments shown and described herein. Distal end 822 iscomprised of multiple lumens 891. The inner portion of these structuresis formed by ribs 890 which act to increase resistance to collapse andkinking of distal end 822. Thin wall sections 826 are compliant andtransfer the outside pressure to second liquid 834 and gel-like material830 contained within the lumens 891. In some embodiments, the distal 2-4mm of feature 892 is filled with gel-like material 830, while theremaining portion is filled with second liquid 834.

FIG. 9 illustrates generally, by way of example, but not by way oflimitation, one embodiment of distal end 922 of the pressuretransmission catheter showing ruggedizing feature 992. A stent-likeinsert 993 is placed within relatively compliant thin wall section 926,to provide a reinforcing structure that provides resistance to kinkingand collapse of distal end 922. Stent 993 may be fabricated from a metaltube (for example, nickel titanium alloy (Nitinol), titanium, 316stainless steel, or platinum) that is, for example, laser cut, etched,or machined to form openings through which thin wall section 926 isdirectly exposed to second liquid 934 and gel-like material 930. Stent993 may alternately be formed, for example, from a wire, a plastic,polymer (for example, acetal resin, polytetra fluorethane, polyethylene,polyurethane, polypropylene, polyamide, polyimide, or acetyl butadienestyrene) and other relatively rigid materials. Stent openings 994 aresized appropriately such that thin wall section 926 can efficientlytransfer the dynamic components of the pressure signal into secondliquid 934 and gel-like material 930 in order to obtain a high-fidelityreproduction of the desired pressure signal. In other embodiments, stent993 is placed on the outside of thin wall section 926. In otherembodiments, stent 993 is molded directly into the distal end.

It may be desired to use the catheter with physiological sensor as aguidewire. It may also be desired to use the catheter with physiologicalsensor as a stand-alone diagnostic catheter; that is, used without firstplacing a therapeutic catheter within the vasculature. For these uses,the catheter with physiological sensor must be able to traverse narrow,tortuous vasculature (such as coronary arteries). Because of this, itmay be desired that the catheter distal tip be very flexible andresilient to kinking, as well as non-injurious to the vasculature. FIG.10 illustrates generally, by way of example, but not by way oflimitation, one embodiment of distal end 1022 of the pressuretransmission catheter showing flexible tip feature 1088. In oneembodiment, flexible tip feature 1088 consists of a spring-like feature1097 terminating in a smooth head 1098. The spring-like feature 1097 isattached to distal end 1022, for example, by wrapping over, slidinginside, and/or molded into distal end 1022. In one embodiment, flexibletip feature 1088 is up to 3 cm long.

FIGS. 11A and 11B illustrate generally, by way of example, but not byway of limitation, one embodiment of distal end 1122 of the pressuretransmission catheter showing flexible tip feature 1188. Flexible tipfeature 1188 comprises a spring-like feature 1197, a smooth head 1198,and a cone-shaped insert 1195. Cone-shaped insert 1195 is perforatedwith numerous holes 1196 to allow gel-like material 1130 movement and toallow gel-like material 1130 to be exposed to the pressure environment.The cone-shaped insert 1195 is inserted into distal end 1122.

FIG. 12 illustrates generally, by way of example, but not by way oflimitation, one embodiment of distal end 1222 of pressure transmissioncatheter showing flexible tip feature 1288. This embodiment is similarto the embodiment shown in FIG. 10. For convenience, similar componentsare not described here. In this embodiment, thin-wall section 1226 hasthe addition of numerous slits 1299 in the portion that is filled withgel-like material 1230. The addition of slits 1299 is to allow more ofthe gel-like material 1230 to respond to the pressure environment, andto allow the tip to be more flexible.

FIG. 13 shows a side view in partial cross-section illustratinggenerally, by way of example, but not by way of limitation, and anenvironment in which it is used, one embodiment of portions of acatheter with physiological sensor 1310 which comprises generally apressure transducer/electronics assembly 1373 and pressure transmissioncatheter 1314. Pressure transmission catheter 1314 is shown as used witha therapeutic/diagnostic catheter 1350. Transmission catheter 1314 isinserted into lumen 1356 of therapeutic/diagnostic catheter 1350. Thisis done by inserting distal end 1322 of pressure transmission catheter1314 into lumen 1356 and slidably moving through lumen 1356 until distalend 1322 projects beyond distal end 1351 of the therapeutic/diagnosticcatheter.

In one embodiment, the therapeutic/diagnostic catheter 1350 includes anelectrode 1372 with connection 1376 to external connection 1383.Electrode 1372 is attached or made part of catheter 1350 such that whencatheter 1350 is in use, electrode 1372 can be used to sense a referencephysiological, electrical signal needed for particular therapies anddiagnoses. In this embodiment, the signal from reference electrode 1372is compared with the signal from the catheter electrode. Providingreference electrode 1372 on catheter 1350 negates the need for the useof external electrodes to measure, for example, an electrocardiogram(ECG) that are prone to inaccurate measurement, noise, anddisconnection. Reference electrode 1372 may be provided on catheter1350, for example, by attachment, as a molded in place part or feature,or as a deposition or coating.

FIG. 14 illustrates generally, by way of example, but not by way oflimitation, and an environment in which it is used, one embodiment ofportions of a pressure and electrical sensing catheter 1410 with atypical therapeutic catheter 1450, in this case an intra-aortic ballooncatheter (e.g., Profile® 8 FR. Intra-Aortic Balloon (IAB) Catheter,Datascope Corporation, Fairfield, N.J.). An opening is typically made inone of the femoral arteries 1460 into which is inserted a guidewire (notshown), which is long, thin, and flexible. The guidewire is threaded upthrough the abdominal aorta 1464 to the descending thoracic aorta 1468.Once the guidewire is correctly placed within the vasculature,therapeutic catheter 1450 is threaded over a guidewire (not shown) andadvanced to the treatment site. The guidewire is then removed. Pressuretransmission catheter 1414 is advanced through a lumen of catheter 1450until distal end 1422 projects beyond distal end 1451 of catheter 1450.This allows the pressure and electrical measurements to be taken on theupstream (high pressure) side of intra-aortic balloon catheter balloon1452. The pressure transmission catheter 1414 terminates at the pressuretransducer/electronics assembly 1473 which is connected through cable1475 to the intra-aortic balloon catheter control system 1454. Theintra-aortic balloon catheter 1450 terminates at control system 1454.Catheter electrode 1436 senses an electric signal from the heart 1470,e.g., an electrocardiogram signal, which is used by control system 1454to trigger inflation and deflation of balloon 1452. Balloon 1452, wheninflated, displaces blood in the artery. If timed correctly, thisresults in an increase in systolic pressure and increased perfusion ofthe coronary arteries (not shown). The pressure measurements are used tocalibrate control system 1454 to take into account the time lag betweenthe electrical impulse from the heart 1470 and cardiovascular response.

Some disclosed embodiments of the catheter with physiological sensorprovide a prefilled catheter-based pressure sensing system that cantraverse a lumen of a diagnostic/therapeutic catheter. Previous pressuresensing catheters, especially those used with intra-aortic balloons, arenot suitable because they are either too large, too compliant to provideaccurate pressure measurements, too expensive, too inconvenient to use,and/or have other limitations, particularly those associated with beingnon-prefilled. Prefilling provides the added assurance of high qualitycontrol, reduced preparation time prior to use, and greatly reducedlikelihood of air bubbles in the lumen. Additionally, a less complex andmore accurate and reliable system for detecting electrical signals isprovided for treatments requiring the detection of such signals.

Existing devices gather control data using separate electrodes. Theseelectrodes sense an electric signal to control therapeutic catheters,such as the inflation/deflation of an intra-aortic balloon catheter.These separate electrodes are prone to electrical interference, are notprecise in electrical detection, and are prone to environmental affectsand accidental disconnection. These separate electrodes typically mustbe placed away from the target site, and therefore do not preciselymeasure the desired signals. Some embodiments of the disclosed pressureand electrical sensing catheter provide the ability to gather pressuremeasurements beyond the intra-aortic balloon catheter balloon locationduring the entire treatment period as well as providing electricalsignals to the balloon control system, making separate electrodesunnecessary. Since the catheter electrode is placed at the target site,the desired electrical signal is measured, minimizing multiple signalsand electrical noise associated with surface skin electrodes. In someembodiments, the catheter electrode is also an integral part of thecatheter and therefore cannot be accidentally disconnected.

The disclosed embodiments provide an apparatus that obtains bloodpressure measurements that are reliable and of high quality. Such animproved catheter capable of providing reliable high-fidelity bloodpressure signals could also open up the possibility of implementingclosed loop control, eliminating the need for manual adjustments of thetiming of balloon inflation based on observation of the measured bloodpressure waveform. Some embodiments of the pressure sensing catheterembodied here are also useful as diagnostic catheters for measurement ofleft ventricular pressure of the heart. For example, a guiding cathetercontaining a lumen of sufficient size to accommodate the disclosedpressure sensing catheter could be directed transvascularly into theleft ventricle. The guiding catheter could be any of a series ofstandard catheters that are currently used for crossing the aortic valveretrograde into the left ventricle.

In another embodiment, the distal tip of the catheter with physiologicalsensor incorporates a flexible tip to allow the catheter to be guidedinto narrow, tortuous vasculature, such as coronary arteries, with orwithout a guiding catheter. This would allow the catheter to assessstenosis severity by measuring fractional flow reserve.

In some embodiments, the catheter with physiological sensor has anadvantageously very low compliance. The catheter can be fabricated witha compliant thin wall distal end, and all or most of the thin-walldistal end can be exposed to the body fluid. By using a compliantmaterial on the distal end, the pressure signal can be transmittedthrough the compliant material into the catheter lumen and transmittedby the catheter liquid. In embodiments where the pressure transducer andmain portion of the catheter have a significant compliance, the thinwall compliant distal end design results in better frequency responsethan can be achieved if the pressure signal were transmitted to thelower-viscosity catheter liquid through only the viscous gel-likematerial.

In some embodiments, the catheter with physiological sensor may be usedsuch that pressure measurements may be taken beyond thetherapeutic/diagnostic catheter lumen tip as well as at some pointbetween the distal and proximal ends of the catheter. For example, anopening in the therapeutic/diagnostic catheter could be made at a pointalong its length through which pressure measurements may be taken.

CONCLUSION

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A pressure sensing device comprising: a pressure transducer; and apressure transmission catheter comprising: an elongate structure formedto define an internal lumen extending from a distal sensing portion ofthe pressure transmission catheter to a proximal end of the pressuretransmission catheter in fluid communication with the pressuretransducer, wherein the pressure transmission catheter is constructed toprovide no transfer of fluid between the internal lumen and spaceoutside of the pressure sensing device; a pressure-transmitting liquidcontained within the internal lumen; support structure formed tosurround the internal lumen at the distal sensing portion to preventcollapse of the internal lumen by lateral pressure forces, the supportstructure further being formed to define a plurality of openings throughthe support structure, the plurality of openings comprising at least oneopening that is laterally facing; and diaphragm structure formed inrelation to the support structure to provide a diaphragm portion foreach of the support structure openings.
 2. The pressure sensing deviceaccording to claim 1, wherein the diaphragm structure comprises acompliant membrane formed around at least lateral outside surfaces ofthe support structure and over any of the openings that are laterallyfacing.
 3. The pressure sensing device according to claim 2, wherein oneof the openings of the support structure is at a distal longitudinal endof the pressure transmission catheter.
 4. The pressure sensing deviceaccording to claim 3, wherein the diaphragm structure comprises a gelplug to cover the opening in the support structure at the distallongitudinal end.
 5. The pressure sensing device according to claim 1,wherein a plurality of the support structure openings are laterallyfacing.
 6. The pressure sensing device according to claim 1, wherein theelongate structure comprises a material selected from the groupconsisting of polyamide, polyimide, impregnated plastic, polytetrafluoroethylene, polyethylene, polyurethane, polyvinyl chloride, andpolypropylene.
 7. The pressure sensing device according to claim 1,wherein the elongate structure comprises a metal selected from the groupconsisting of 316 stainless steel, Nitinol, titanium, MP35N, and MP52.8. The pressure sensing device according to claim 1, wherein a distalend of the elongate structure comprises a thin-wall portion, the supportstructure is disposed over the thin-wall portion, and wherein pressureis referred though the laterally facing openings to the pressuretransmitting fluid through the thin-wall portion.
 9. The pressuresensing device according to claim 1, wherein the pressure transmittingliquid is selected from the group consisting of water, saline,fluorinated hydrocarbon, silicone oils, alcohols, and propylene glycoldispersed in water.
 10. The pressure sensing device according to claim1, wherein at least a portion of the elongate structure is electricallyconductive.
 11. The pressure sensing device according to claim 10,wherein the elongate structure is substantially covered with aninsulating material.
 12. The pressure sensing device according to claim1, wherein a distal end of the elongate structure includes anelectrically conductive portion which acts as an electrode for detectingan electric signal.
 13. The pressure sensing device according to claim12, and further including a conductor that is coupled to theelectrically conductive portion and disposed along the length of theelongate structure.
 14. The pressure sensing device according to claim1, wherein at least two liquids are disposed within the internal lumen.15. The pressure sensing device according to claim 1, wherein thepressure transmission catheter is adapted for implantation.
 16. Thepressure sensing device according to claim 1, further comprising animplantable housing, and wherein the pressure transducer is mountedwithin the implantable housing.
 17. The pressure sensing deviceaccording to claim 1, wherein the pressure transducer is coupled to anelectrical lead.
 18. The pressure sensing device according to claim 17,wherein the electrical lead provides input power.
 19. The pressuresensing device according to claim 17, wherein the electrical leaddelivers output signals to a control system.
 20. The pressure sensingdevice according to claim 17, wherein the electrical lead deliversoutput signals to a therapeutic system.
 21. The pressure sensing deviceaccording to claim 1, wherein the elongate structure comprises abiocompatible material.
 22. The pressure sensing device according toclaim 1, wherein a distal end of the elongate structure furthercomprises a thin-wall portion.
 23. The pressure sensing device accordingto claim 1, wherein at least two liquids are disposed within theinternal lumen, and wherein the at least two liquids comprise: a firstliquid in communication with the pressure transducer; and a secondliquid in communication with the diaphragm structure and the firstliquid, and wherein the first liquid and the second liquid are notsoluble with each other and together substantially fill at least aportion of the internal lumen.
 24. The pressure sensing device accordingto claim 1, wherein the diaphragm structure is comprised of a compliantmaterial.
 25. The pressure sensing device according to claim 1, whereina distal end of the elongate structure includes a plurality of ribs. 26.The pressure sensing device according to claim 1, wherein the a distalend of the elongate structure further comprises a plurality of holes.27. The pressure sensing device according to claim 26, wherein thediaphragm structure is disposed over the plurality of holes.
 28. Thepressure sensing device according to claim 1, further comprising aflexible tip comprising: a coil having a first end and second end; arounded head; and wherein the rounded head is coupled to the first endof the coil, and the second end of the coil is coupled to a distal endof the elongate structure.
 29. The pressure sensing device according toclaim 1, further comprising a flexible tip comprising: a coil having afirst end and a second end; a rounded head; a cone-shaped insert havinga plurality of holes; and wherein the rounded head is attached to thefirst end of the coil, and the second end of the coil is attached to thecone-shaped insert and wherein the cone-shaped insert is inserted into adistal end of the elongate structure.
 30. The pressure sensing deviceaccording to claim 1, wherein the support structure is integral with athe distal end of the elongate structure.
 31. The pressure sensingdevice according to claim 1, wherein the support structure is integralwith a the distal end of the elongate structure, and wherein theplurality of openings comprise thin areas of the elongate structure tubewhere material was removed.
 32. The pressure sensing device according toclaim 1, wherein a distal end of the elongate structure comprises athin-wall portion, the support structure is disposed interior of thethin-wall portion, and the diaphragm structure comprises the thin-wallportion.